1. Field of the Invention
The present invention relates to an image forming apparatus wherein an image is formed with an information beam which corresponds to the information signal to be recorded.
2. Description of the Prior Art
In the apparatus of this type, a beam repeatedly scans a photosensitive member in a major scanning direction with the use of beam deflecting means, such as a polygonal mirror and a galvanomirror, while at the same time, the photosensitive member is moved in a minor scanning direction. Thus, the photosensitive member is scanned along a number of scanning lines spaced regularly, so that an image is formed thereon in accordance with the information signals.
On the other hand, it has been proposed in the field of copying machines, as disclosed in U.S. Pat. No. 4,284,345, for example, that the apparatus is formed with a first assembly and a second assembly, the former being supported on the second assembly rotatably about a shaft, so as to facilitate the maintenance or servicing to the internal elements or parts around the photosensitive member and to facilitate the removal of jammed transfer materials from the apparatus. Such a proposal has been put into practice particularly in small sized copying machines.
This type of copying machine does not have sufficient mechanical rigidity as a whole of the apparatus, with the result that there easily occur vibrations within the apparatus upon the occasion of an external vibration or a vibration of a movable member in the apparatus. Those vibrations hardly influence the quality of the resultant image in the copying machines wherein an original is directly imaged on the photosensitive member through a lens.
However, the vibrations cannot be neglected in the image forming apparatus of the type wherein the photosensitive member is scanned in the major scanning direction by a beam modulated in accordance with the information signal to be recorded and scanned in the minor scanning direction by moving the photosensitive member in the minor scanning direction. That is, when the vibration of the optical system, particularly that of the deflecting means, becomes large, the pitches between the scanning lines, which must be constant, may vary and the speed of the beam scanning in the main scanning direction may also vary so that the resolution of the resultant image is degraded.